The invention refers to a system for measuring the duration ratio of pulses of variable frequency, particularly in electronically controlled fuel-injection systems for internal combustion engines.
For the measuring of the duration ratio (pulse width/period), particularly in electronically controlled fuel-injection systems for internal combustion engines, methods have become known in which two separate counters are used. The period is determined by the first counter while the pulse width is measured with the second counter. The ratio of the results of the two measurements is then formed by an arithmetic operation.
When this method is used it is necessary to establish the resolution of the result in advance as a function of the input frequency. In particular, if the frequency of the pulse to be measured is subject to large variations, then in view of low frequencies, a design of the period counter with a very high capacitance is necessary so that no overrun takes place if one still wishes to obtain a resolution which is still satisfactory at high frequencies.